Question

The molecular formula of diphenyl methane \(\left(\mathrm{C}_{6} \mathrm{II}_{5}\right)_{2} \mathrm{CII}_{2}\) is \(\mathrm{C}_{13} \mathrm{II}_{12}\). IIow many structural isomers are possible when one of the hydrogen is replaced by chlorinc atom? (1) 6 (2) 4 (3) 8 (4) 7

Short answer

8 distinct isomers

Step-by-step solution

- Understanding the Molecular Structure

The molecular formula of diphenyl methane is \(\text{(C}_6\text{H}_5\text{)}_2\text{CH}_2\), which simplifies to \(\text{C}_{13}\text{H}_{12}\). This means there are two benzene rings connected by a \(-\text{CH}_2-\) group.

- Identifying Possible Substitution Sites

Each benzene ring has 5 available hydrogen atoms that can be replaced by chlorine. Since there are two benzene rings, we initially consider \(5 + 5 = 10\) substitution sites.

- Recognizing Symmetry

Due to the symmetry in the structure of diphenyl methane, some substitutions will result in identical isomers. Identifying these symmetric positions is crucial to count distinct isomers.

- Counting Distinct Isomers

On each benzene ring, substitution at positions 1, 2, 3, 4, and 5 must be considered separately. For one ring, the substitution at position 1 is unique, but positions 2 and 6 are equivalent, as are positions 3 and 5. Therefore, each ring has 4 unique positions (1, 2, 3, 4). So combining the substitutions from both rings, there are \(5 + 4 = 9\) potential isomers. Then we must consider the symmetry with the bridging \(-\text{CH}_2-\), which reduces one isomer. Hence, we get 8 distinct isomers.

Key concepts

molecular structure

The molecular structure of a compound defines how its atoms are arranged and connected. Diphenyl methane, also known as \(\mathrm{(C}_6\mathrm{H}_5\mathrm{)}_2\mathrm{CH}_2\), simplifies to \(\mathrm{C}_{13}\mathrm{H}_{12}\). This means it has two benzene rings connected by a single \(\mathrm{-CH}_2-\) group.
Understanding this is crucial as it helps us visualize how atoms are linked and where substitutions can occur. In this case, each benzene ring has hydrogen atoms that can potentially be replaced by a chlorine atom.
By knowing the molecular structure, we can identify possible substitution sites and predict how the molecule's properties will change with different substitutions.

substitution reactions

Substitution reactions in organic chemistry involve replacing an atom or a group of atoms in a molecule with a different atom or group. For diphenyl methane, we are interested in replacing one hydrogen atom with a chlorine atom.
Each benzene ring in diphenyl methane contains five hydrogen atoms that are available for substitution. These reactions change the molecule's physical and chemical properties.
For example, replacing a hydrogen with chlorine might affect the molecule’s polarity, solubility, or reactivity. Understanding where substitutions can happen helps in predicting and explaining the product's behavior in various chemical contexts.

symmetry in chemistry

Symmetry plays a significant role in determining the uniqueness of molecules. In diphenyl methane, symmetry comes into play when we consider where to substitute the hydrogen atom.
Due to symmetry, certain positions on the benzene rings give rise to identical isomers. For instance, positions 1 and 4 on each benzene ring are unique, but positions 2 and 6 (or 3 and 5) are equivalent due to the molecule’s symmetrical nature.
This symmetry reduces the number of distinct isomers we need to consider. Recognizing symmetrical positions helps us avoid counting identical isomers multiple times.

isomer counting

Isomer counting involves determining how many distinct molecules can be formed by substituting atoms in different positions. For diphenyl methane, this means counting how many unique chlorinated versions of the molecule we can create.
Each benzene ring has five positions, but due to symmetry, we only count four unique positions per ring. Combining both rings, we initially have 9 possible sites, but we must account for substitutions that create identical isomers.
By carefully combining these positions and considering symmetry, we reduce the total to 8 distinct structural isomers. This knowledge helps in predicting the number of unique compounds we can synthesize, useful in fields like drug development and material science.